The evidence provided by the noble gases for a magmatic gas component in the Northwest Geysers adds new constraints to genetic models of the system and its evolution. The high proportion of magmatic gas and high total NCG in HTR steam are inconsistent with an origin of the vapor-dominated Northwest Geysers reservoir from deep boiling of a connate or metamorphic water. Instead, the strong magmatic component suggests that the HTR and the sharp HTR/NTR boundary observed in the Northwest Geysers reservoir were formed and are sustained by an active flux of magmatic volatiles.